Relapsed leukemia is chemotherapy resistant, survival is poor, and the molecular mechanisms underlying resistance remain poorly understood. Recurrent mutations in the chromatin modifier SETD2 were recently described to be enriched in relapsed pediatric acute lymphoblastic leukemia patients (Mar et al, 2014). Preliminary data suggests that SETD2 loss leads to chemotherapy resistance through impaired DNA damage response (DDR) and a resultant failure to trigger apoptosis to DNA damaging agents. The goal of the proposed research project is to characterize the chemotherapy resistance associated with SETD2 loss and define its mechanism of action. To better understand the resistance induced by SETD2 loss and its relevance to leukemia, this proposal utilizes several newly developed in vitro and in vivo models of SETD2 loss, including a novel conditional murine knockout of Setd2 and engineered isogenic leukemia cell lines with SETD2 loss. Leukemia chemotherapy agents with different mechanisms of inducing cell death, including various types of DNA damage, will be used in these models of SETD2 loss to gain insight into the potential defects in DNA damage signaling. Findings in vitro will be studied in vivo to understand how a more physiological leukemia engraftment and chemotherapy exposure alters therapy resistance. The mechanism of resistance will be elucidated by closely examining the components of the DDR, the requirement for SETD2 catalytic function and how SETD2 loss affects the local chromatin distribution of DDR mechanisms and DNA damage. In summary, SETD2 loss is a novel mechanism of chemotherapy resistance in leukemia, and this proposal seeks to substantially advance our understanding of this clinically relevant lesion. Candidate: Dr. Brenton Mar is an instructor in Pediatric Hematology/Oncology at Boston Children's Hospital who aims to become an independent tenure track physician-scientist working on roles of epigenetic regulators in leukemogenesis and chemotherapy resistance. He has outlined a 5 year period of mentored training to strengthen his skills in disease modeling and functional genomics. This training period will be carried out under the mentorship of Dr. Benjamin Ebert, a recognized leader in leukemia biology and hematopoiesis. He has also assembled an advisory committee composed of Dr. Alan D'Andrea, Dr. James Griffin, Dr. Lewis Silverman and Dr. Charlie Roberts that will help guide him in his training and research. Environment: The Dana-Farber Cancer Institute and Boston Children's Hospital in the Harvard Medical area have an internationally recognized research program in Pediatric Hematology/Oncology with areas of expertise in hematopoiesis, epigenetics, transcription, DNA damage response, tumor biology, and the genetics of hematologic and malignant diseases. Intellectual interactions and collaboration are fostered by weekly research seminars. The division has a long track record of mentorship and producing the nation's leaders in hematology and oncology research.